The present invention relates to a method for preparing a surface for adhesive bonding, particularly an aluminum surface.
The integrity of adhesively bonded joints to aluminum substrates is very dependent upon preparation and priming of the aluminum surfaces to be joined. Acid etch techniques, such as FPL etch (sulphuric acid), chromic acid etch or Pasa Jel (phosphoric acid) etch, were used together with various primers to prepare aluminum surfaces for adhesive bonding. Recently, a phosphoric acid anodizing process has been developed which employs a phosphoric acid etch under an electrical potential to provide a stable oxide layer on the surface of aluminum substrates. Both tank and non-tank anodizing techniques have been developed. This process, when used together with corrosion-inhibiting primers, is generally considered to be the state of the art surface preparation for aluminum adhesive bonding.
Although the phosphoric acid anodizing process provides excellent surface preparation for adhesive bonding, the process has drawbacks. The process requires acid etching and the use of chromates in pretreatment and in primers. An electric potential similar to electroplating is required. Use of the process in a factory introduces problems with personnel safety and waste disposal. Use of the process in the field further introduces problems of corrosion, as when the acid is not properly and completely removed, and safety. Because of these problems, the non-tank technique is generally not used in field level maintenance.
The method generally used in field maintenance consists of dry abrading the surfaces to be joined, followed by adhesive bonding. This method does not provide a quality bond with acceptable durability.
Accordingly, it is an object of the present invention to provide a method for preparing an aluminum surface for adhesive bonding.
Other objects, aspects and advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description of the invention.